1. Field of the Invention
The present invention is related to the field of containers. In particular the present invention relates to a method and apparatus for manufacturing a hot-fill container having a tapered body and dome.
2. Description of the Related Technology
Plastic containers are frequently used due to their durability and lightweight nature. Polyethylene terephthalate (PET) is used to construct many of today's containers. PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
PET containers are used for products, such as beverages and semi-solid foods. Often these liquid products, such as juices, isotonics and sauces, are placed into the containers while the liquid product is at an elevated temperature, typically between 68° C.-96° C. (155° F.-205° F.) and usually about 85° C. (185° F.). When packaged in this manner, the hot temperature of the liquid is used to sterilize the container at the time of filling. This process is known as hot-filling. The containers that are designed to withstand the process are known as hot-fill containers.
A variety of methods can be used to manufacture PET containers. One such method is called the “two-step” process. The “two-step” process first involves forming a plastic preform for use in the blow molding process.
A plastic “preform” is typically a tubular shaped object that comprises a finish, a neck and body. The preforms are then placed into molds and subjected to the blow molding process. This step may be formed at some point later in time. The two step blow molding process is used in order to manufacture large amounts of containers using the preforms.
Another type of blow molding process is a one step blow molding process. The one step blow molding process, in contrast to the two step blow molding process discussed above, involves forming the preform and the finished container without the need to cool the preform fully to form the preform such as in the two step process discussed above. Instead the preform in the one step blow molding process is only cooled to the point in which it can be removed from the mold. The formed preforms in the two step blow molding process are then immediately subjected to the blow molding process.
The blow molded containers may then be filled, with either a cold fill or alternatively, hot-filled. After being hot-filled, the hot-filled containers are capped and allowed to reside at about the filling temperature for a predetermined amount of time. The containers and stored liquid may then be cooled so that the containers may be transferred to labeling, packaging and shipping operations. As the liquid stored in the container cools, thermal contraction occurs resulting in a reduction of volume. This results in the volume of liquid stored in the container being reduced. The reduction of liquid within the sealed container results in the creation of a negative pressure or vacuum within the container. If not controlled or otherwise accommodated for, these negative pressures result in deformation of the container which leads to either an aesthetically unacceptable container or one which is unstable. The container must be able to withstand such changes in pressure without failure.
The negative pressure within the container has typically been compensated for by the incorporation of flex panels in the sidewall of the container. Traditionally, these paneled areas have been semi-rigid by design and are unable to accommodate the high levels of negative pressure generated in some lightweight containers. Currently, hot-fill containers typically include substantially rectangular vacuum panels that are designed to collapse inwardly after the container has been filled with hot product. These flex panels are designed so that as the liquid cools, the flex panels will deform and move inwardly. The adjacent portions of the container, such as the so-called lands, or columns, which are located between, above, and below the flex panels, are intended to resist any deformations which would otherwise be caused by hot-fill processing. Wall thickness variations, or geometric structures, such as ribs, projections and the like, can be utilized to prevent unwanted distortion. Generally, the typical hot-fillable container structure is provided with certain pre-defined areas which flex to accommodate volumetric changes and certain other pre-defined areas which remain unchanged.
During the fill process, existing machinery typically only permits two points of contact, which typically are located on the body of the container. The need to have the points of contact located on the body results in a restrictive geometry and shape for containers that have domes. This is because the dome needs be shaped in order to avoid interfering with the machinery that grips the containers on the fill line. Therefore, there exists a need in the field to have a container that is able to use differently shaped domes that are able to accommodate having a point of contact located on the dome so as to permit more varied design in the construction of plastic containers.